Biochemical and physiological studies in vitro and in retina-specific ABC transporter (ABCR) -/- knockout mice suggest that ABCR accelerates recovery of rod photoreceptor resensitization after intense light exposure by transporting isomerized chromphore, all-trans-retinal, across the rod outer segment disk membrane. The current proposal is to test hypotheses about the role of ABCR in human disease as follows: (1) Study the visual cycle abnormalities in patients with retinopathy due to ABCR mutations with the goals of dissecting the contributions of primary rod effects vs. secondary disease consequences and learning the relationship between primary rod abnormalities and the genotype; (2) Investigate the basis of rod visual loss in these patients by testing the hypothesis that desensitization by equivalent light contributes to the visual loss, and determine if short term trial of unilateral light reduction can alter rod sensitivity and select mutations; (3) Test whether heterozygotes of ABCR mutations show visual cycle abnormalities and to approach from the visual function perspective the issue of ABCR sequence variance as risk factors in age related macular degeneration.